When Barack Obama met John McCain in their first debate, on Sept. 26, 2008, Obama promised to free the U.S. from dependence on Middle East oil within a decade. He said he would “deal with” Pakistan to force more action against Taliban safe havens. And he decried McCain’s proposal to tax health care benefits “for the first time in history.”

Four years later, Middle East energy independence is still a distant goal. Pakistan’s government is as two-faced — and handsomely subsidized by the U.S. — as ever. When it came time to fight for his health care plan in Congress, Obama supported taxing health benefits. For the first time in history, apparently.

This isn’t to pick on Obama, who happens to be the man in a position to deliver on his pledges. McCain would surely have fallen short himself. (His incorrectly predicted that Obama would meet with, and get rolled by, the likes of Hugo Chávez and Mahmoud Ahmadinejad.) The point is to follow Wednesday’s debate between Obama and Mitt Romney with a decidedly skeptical ear.

It’s not that the debates are all empty talk. In his 2008 sessions with McCain, Obama also vowed to reform the country’s health care system. He promised a new push to support renewable energy. He called for Wall Street reform, pledged middle-class tax cuts and said he’d leave Iraq and send more troops to Afghanistan. He delivered on all those things, and fought unsuccessfully for others.

But such detailed plans rarely make it past the Inauguration intact. The world changes. Congress has its say. The political winds shift. Obama may have meant it in his second debate with McCain when he said, “We’re going to have to take on entitlements, and I think we’ve got to do it quickly.” But he hardly charged into that breach. And although liberals are understandably ridiculing Paul Ryan for dodging the details of the Romney-Ryan budget plan — whose basic math seems not to add up — Ryan also has a point when he says the specifics depend on the whims of an unpredictable Congress (whose partisan makeup remains uncertain, no less).

Unfortunately, the substance of the debates is often secondary anyway. By the time they roll around, the candidates’ agendas are familiar to all but the most checked-out voters. (Yes, there are surely some people who have ignored most of the campaign to date and are willing to tune in for 90 minutes of policy talk. But probably not many.) The result can be tedium. Do you remember that first Obama-McCain debate? Do you clearly remember any of them? Probably not.

The exception proves the rule: it’s easy to remember 2008’s one vice-presidential debate, between Joe Biden and Sarah Palin, forever famous for her multiple winks at the camera. That’s because we process these debates with our reptilian brain. We watch for moments of conflict, wit, fallibility. In theory, debates are edifying exchanges and arguments. In reality, they often wind up being a form of jousting that helps viewers form judgments about the candidates’ true nature and character.

Whom does that favor? It’s difficult to say. Obama has the quicker wit, but also four pretty rough years to explain away. Romney survived more than one “do or die” debate in the primaries, but he was helped by his opponents’ ineptitude.

But remember: this is only the first of three presidential debates. As Gallup has noted, several recent “winners” of the first debate, as measured by quick reaction polls, went on to lose the election — sparing them the burden of making good on all those bold promises.